* To increase the sales of armaments abroad as a stimulus to national production and development of technology, and to benefit the country's economy through much-needed foreign-exchange earnings and the training and employment of skilled labor.

Once a sale abroad is proposed, it is submitted to the Council for National Security, which weighs the political, diplomatic, military, and commercial aspects. After approval - and there are very few rejections - the sale becomes a simple routine execution of the terms of the contract between the Brazilian manufacturer and the foreign buyer. The Brazilian government does not interfere.

For obvious reasons, there are no disclosures of the deals, and details are kept secret. Such secrecy is considered essential here, in the drive to compete in the world's arms market, totaling well over $100 billion annually.

Brazil is in a fortunate position of having no open enemies or frontier problems with its neighbors, which facilitates its open-door arms sales policy.

The minister of aviation, Brig. Jardim de Mattos Delio, sums it up in even more direct terms: ''The Brazilian arms industry produces to sell. If a customer appears from Soviet Russia, Japan, or China who wants to buy, we will sell.''

Brazilian President Joao Figueiredo, asked recently about Venezuela's possible reaction to Brazil's reported sale of war equipment to Guiana, which has a longstanding border dispute with Venezuela, shot back: ''They can object. We sell to whoever wants to buy.''

Apparently Turkish Cypriot pleas earlier this year for Brazil to sell no arms to the Greek Cypriots fell on deaf ears.

This commercial attitude of selling to anyone who can pay, differs, of course , from the policies followed by the United States and the Soviet Union, by far the world's largest arms suppliers, for which monetary considerations are usually secondary to their political and strategic interests.

Brazil started its armaments industry practically from scratch only several years ago to equip its own armed forces. This happened after the US imposed bans on some equipment sales to Brazil. The US was formerly Brazil's chief arms supplier. Brazil had a military aid program which it abrogated unilaterally, to Washington's surprise.

The International Defense Review, published in London, estimates that with exports reaching $2 billion, 35 percent over 1981, Brazil is probably in fifth place as an arms exporter. Naturally it is well below the US, USSR, France, and West Germany, which produce the costly, highly sophisticated aircraft, rockets, and other weapons. Brazil's weapons exports are still predominantly of conventional types. Still, Brazil already possesses the biggest and most advanced arms industry in the third world, selling to over 30 countries, including nations in Latin America, Africa, the Middle East, and Southeast Asia. Arms sales are on the way to becoming Brazil's top export.

The Brazilian armament industry is both in government and private hands. The government, however, gives encouragement to private enterprise through extension of technical and financial assistance. It maintains numerous highly specialized technical teams staffed by armed forces experts.

In its efforts to improve operations and increase exports, the government only last month appointed the first civilian, Jose Luiz Whitaker Ribeiro, to head the Army's most important armament complex, Imbel. This includes the Army's Technological Center, which serves as coordinator for production and commercialization for the entire industry.

Mr. Ribeiro will combine his new position with the presidency of Engesa, a successful large private company he founded and controls, which produces 50 percent of all the world's armored cars and light tanks on wheels. He is expected to become the overall boss of the armament industry.

Brazil produces a wide variety of arms, such as semiautomatic and automatic rifles, machine guns, cannons, and ammunition of all types and caliber. These have won widespread acceptance for their quality and prices.

Production is about to start of heavier 40-ton tanks on caterpillar treads; Tiger-Fish torpedoes, in cooperation with the British Marconi group; new automatic carbines of the type used by the North Atlantic Treaty countries; 9 -millimeter submachine guns; antitank electronic missiles; anti-airport bombs; and 600-millimeter guided missiles capable of carrying 660 pounds of explosives.

Only recently, a giant Russian-made Ilyushin 76 belonging to the Iraqi Air Force landed at the military airport of the Technical Aerospace Center outside Sao Paulo and picked up 40 tons of war materiel. The purchase was principally antipersonnel and antitank missiles made by Avibras, launchable from ground or air, and considered the most efficient conventional missiles available. These missiles were probably used by the Iraqis against Iran in recent battles.

Iraq is one of Brazil's best clients. Its war orders have grown from a reported $280 million in 1980 to $600 million last year, and might soon reach $1 billion. These orders serve to counterbalance Brazil's huge purchases of Iraqi oil. Egypt also proposed exchanging oil for military equipment, especially armored vehicles.

Embraer, Brazil's leading aircraft manufacturer, in addition to its regular diversified line of jet and twin-engine turboprop planes, both for civilian and military use, will begin producing next year a new T-27 model named Tucano for advanced training, ground attacks, and tactical support.

The air forces of 10 countries, including such advanced ones as Canada and Britain, have already expressed interest in purchasing this craft.

Another company, CTA, is completing plans to make a small pilotless jet plane similar to the V-1 used by Germans over England in World War II.

According to London's Institute of Strategic Studies, the Brazilian armed forces are efficient and modern, with 85 percent of their equipment of national fabrication. With the Army numbering 188,000 men and nearly 400,000 reservists, the Navy 47,000, and the Air Force 43,000, Brazil constitutes the strongest military force in Latin America.